1. Field of the Invention
The present invention relates to a device for sensing a temperature differential between a heat source side and a heat sink side of a thermo-electric device and for regulating a current in response to the temperature differential. The present invention also more particularly relates to a device for providing an optimal current to the thermo-electric device and for a more productive operation of the thermo-electric device.
2. Description of the Related Art
Thermo-electric cooling and heating devices are well known in the art and are based on the Peltier effect. The device moves heat from one location to another when current flows through a predetermined semiconductor material having a p and n type semiconductor material or pellets. Historically, thermo-electric devices are used for spot cooling. This is because the material properties and the device operation limit the device's efficiency.
Thermo-electric refrigeration devices are typically made as a module. The module then can be assembled to a larger system using an amount of appropriate heat exchangers. The heat exchangers are incorporated to enhance heat transfer and to minimize losses. Thermo-electric modules are operated under direct current. The direct current should preferably be optimized to gain a best coefficient of performance (COP). The optimal current is related to one or more material properties of the semi-conductor based materials and a temperature differential between a hot and a cold side of the module. The optimal current is expressed as follows.
                              I          ϕ                =                                            (                                                α                  p                                -                                  α                  n                                            )                        ⁢                          (                                                T                  h                                -                                  T                  c                                            )                                            R            ⁡                          [                                                                    (                                          1                      +                                              ZT                        M                                                              )                                                        1                    /                    2                                                  -                1                            ]                                                          Equation        ⁢                                  ⁢        Number        ⁢                                  ⁢        1            where αp and αn are the Seebeck coefficients of the p and n materials respectively, Tc, and Th are the temperatures of the heat source (cold side) and the heat sink (hot side) respectively, and R is the total electrical resistance of the p and n semiconductor material or pellets.
Normally, one thermo-electric module is operated at one current. The current flowing through all of the pellets is thus the same. It has been observed that when the individual modules are large (for example, to deliver large amount of cooling for commercial refrigeration purposes as an example only), significant temperature differential variations are expected on each thermoelectric module. The inventors have observed that the variation of temperature differentials from one pellet to another implies that the entire module cannot be maintained at its most efficient condition. It has been observed that this known problem in the art is aggravated for large size thermo-electric cooling systems where many thermo-electric modules for a large area are used.
It has also been observed that attempts have been made to manipulate a flow pattern and thermally isolate the thermo-electric pellets. This isolation results in a uniform temperature differential (Th−Tc) being maintained for a thermo-electric module. However, the actual temperature differential may not be uniform as expected. A major heat conduction occurs along the thermally conducting but electrically insulating material that is used to prevent the working fluid or an exposed surface from contacting the thermo-electric materials. This conduction results from an electrical insulator with high thermal conductivity (ceramics) that is sandwiched between the thermo-electric pellets and the heat exchangers. This material has a high heat transfer coefficient. This is a known problem and further imposes a difficulty in maintaining the temperature differential along the flow direction.
Accordingly, there is a need for regulation of the power supplied to individual modules that show reasonable temperature uniformity along the fluid flow direction.
Accordingly, there is a need for a modular system for thermo-electric cooling products.